Understanding honey bee colony losses

Four papers published today in the Journal of Apicultural Research describe the results of surveys of beekeepers in 22 countries worldwide. Two present information on losses of honey bee colonies from the 2012-13 winter gathered from a total of more than 22,000 beekeepers together owning nearly 1 million colonies.

The first paper(1) reports colony losses from the USA for the 2012-13 winter. These losses were much higher than reported for the previous year (22.5%), but at approximately 30%, they are exactly average for losses since the recent surveys began in 2006-7. The difference between the last two years highlights the differences in the weather experienced. Amateur beekeepers tended to blame losses on factors which should be within their control, such as starvation, or weak colonies going into winter, whilst commercial beekeepers tended to blame factors outside their control such as pesticides and queen problems. The parasitic mite Varroa was a key factor reported, but the symptoms of “Colony Collapse Disorder” were low down the list of reported causes.

Meanwhile, the second paper(2) reports the results from standardised questionnaires developed by members of the COLOSS research association from 19 mainly European countries. For the first time, the authors have attempted to model the influence of various factors on the losses, with some striking results. Significant factors identified with colony losses were the age of queen bees in colonies going into winter, the treatment of varroa, and access by foraging honey bees to agricultural crops such as oilseed rape and maize. This could support the current concerns about pesticides widely used on these crops, but there is also growing evidence that the decline for bees in areas of intensive agriculture may be because mass flowering crops provide food for only part of the year in a landscape otherwise devoid of bee forage, and also that these crops may provide poor quality food for bees. The third paper(3) documents for the first time colony losses in Luxembourg from 2010-2012. Although a small country, the losses reported seem to fit in well with what is known of losses in neighbouring countries.

Finally, in contrast to these results from the northern hemisphere, the last paper(4) reports data from South Africa. Whilst these losses (29.6%) are comparable with those reported elsewhere, the causes seem to be different. The main cause reported by the South African beekeepers is the Cape honey bee, which acts as a social parasite in colonies of the more common savannah honey bee. The authors emphasise that the causes of colony loss experienced in the northern hemisphere, although present in South Africa, appear to be less threatening there, and uniquely African factors seem to be more significant.

IBRA Science Director and JAR Senior Editor Norman Carreck says: “We are now eight years into the story of increased honey bee colony losses, and these new papers increase our confidence that we are beginning to understand the causes”

3. The paper “A survey on some factors potentially affecting losses of managed honey bee colonies in Luxembourg over the winters 2010/2011 and 2011/2012” by Antoine Clermont and colleagues is available at: http://www.ibra.org.uk/articles/Bee-colony-losses-in-Luxembourg-2010-2012 4. The paper “A survey of managed honey bee colony losses in the Republic of South Africa - 2009 to 2011” by Christian Pirk and colleagues is available at: http://www.ibra.org.uk/articles/Colony-losses-in-South-Africa-2009-11